#include <iostream>
using namespace std;

const int N = 110;

int n;
int f[N][N];

int main()
{
    cin >> n;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= i; j++)
            cin >> f[i][j];

    for (int i = 2; i <= n; i++)
        for (int j = 1; j <= i; j++)
            f[i][j] += max(f[i - 1][j - 1], f[i - 1][j]);

    if (n % 2)
        cout << f[n][n / 2 + 1] << endl;
    else
        cout << max(f[n][n / 2 + 1], f[n][n / 2]) << endl;
    return 0;
}